Project Summary The gastrointestinal (GI) tract has a remarkable diversity, using multiple unique cell types to perform homeostatic functions as well as survey and protect the largest surface in the body. While microbial detection is indispensible in the epithelium and innate immune system, there is mounting evidence that the enteric associated nervous system (EANS) is a pivotal player in detection of luminal composition. The morphology and neurochemical code for the nervous system contained within the intestine (intrinsic) has been extensively characterized, which has led to vital insights into circuitry and function. Innervation from the peripheral nervous system (extrinsic) has been similarly interrogated, but far less is understood regarding circuitry. In total, enteric associated neurons (EANs) provide dense innervation of the small and large intestine, controlling peristalsis, local blood flow, transmucosal fluid exchange, and detection of intestinal inflammation. Recent studies observed that indigenous and foreign bacteria induce changes in EANs. Of particular interest, it has been demonstrated that an attenuated form of Salmonella typhimurium, the mutant spiB, activates enteric- associated sympathetic neurons that release norepinephrine, which in turn alters muscularis macrophage (MM) gene expression towards a tissue-protective, or anti-inflammatory, profile. The presently undefined cellular circuit that results in these changes will be termed microbe neuro-immune reflex loop (MNIRL). While downstream effects of bacteria on EANs have been illustrated, it has yet to be determined how bacteria or their metabolites can activate or cause these changes in EANs. In order to properly dissect this circuit, we will set out to first characterize the basic architectural and genetic map of the EANS, incorporating the effects of the commensal microbiome, utilizing novel imaging and RNA profiling techniques. Upon establishing this EANS map with particular attention to sensory components, we will identify those EANs that are activated by an attenuated strain of Salmonella and possible EAN cellular partners. Finally, taking advantage of cell specific neuro-modulatory technology we will examine the necessity of the MNIRL in the steady-state and during Salmonella infection. We will also determine whether fast responses in immune cell populations are altered with MNIRL manipulation. This study will enhance overall understanding of the EANS and has the potential to change enteric infection or inflammation paradigms, possibly leading to new therapeutic routes.